U.S. Pat. No. 4,652,473 discloses a pressure-sensitive adhesive tape comprising a backing having two separate layers that delaminates. The outer layer has sufficiently high tensile strength to maintain its integrity when removed from the tape and the inner layer adjacent the adhesive is thin and deformable, so that the outer layer can not be removed from the inner layer without disrupting the adhesive bond of the inner layer to the pressure sensitive adhesive, thus providing tamper indication.
U.S. Pat. No. 4,630,891 discloses a tamper resistant security film comprising a monolayer of transparent microspheres supported in a thin layer of binder material. A layer of pressure-sensitive adhesive is coated onto the binder material and at least one patterned layer having differential adhesion to the pressure-sensitive adhesive layer and the binder layer such that upon attempted removal of the film from a substrate at elevated temperature, the film splits, with part of the film remaining on the substrate and part being removed, thus providing tamper indication.
Japanese Patent Applications Publication No. 81JP-06167-8&9 (J57176125A & J57176126A) disclose the extrusion and lamination or coextrusion of a rollable and stretchable thermoplastic resin with a ductile and stretchable thermoplastic resin. The composite is then drawn or stretched monoaxially or biaxially to provide a film which can be delaminated to provide very thin layers of the respective component resin films.
Delaminating films, such as described in the above references include two or more layers of polymeric materials, bonded together either by heat lamination, coextrusion or by means of an adhesive layer. Delamination for these composite films is the separation of the various layers from each other to provide tamper indication. However, the lamination or coextrusion of multiple polymeric layers increases the material expense of the film and tape and requires complex manufacturing techniques.